NullPointerException : JUnit test for Repository - spring-boot

Question

Is it correct to write JUnit test case for Repository like this? Also while running it , Iam getting NullPointerException at line Mockito.when...
here is my test class:
#ContextConfiguration(locations = { "classpath*:resources/invoices-context.xml",
"classpath*:resources/invoices-int-schema.xml" })
public class RoomRepositoryTest {
#Autowired
RoomRepository roomRepository;
private RoomEntity roomEntity;
#Test
public void findRommByDateTest() throws ParseException {
String startDate = "27-07-2020";
sDate = new SimpleDateFormat("dd-mm-yyyy").parse(startDate);
String endDate = "28-07-2020";
eDate = new SimpleDateFormat("dd-mm-yyyy").parse(endDate);
String roomType = "SINGLE";
roomEntity = new RoomEntity();
roomEntity.setRoomId(1);
roomEntity.setRoomPrice(6000);
roomEntity.setRoomStatus("AVAILABLE");
roomEntity.setRoomType("SINGLE");
Mockito.when(
roomRepository.findRoomByDate(Mockito.any(Date.class), Mockito.any(Date.class), Mockito.anyString()))
.thenReturn(roomEntity.getRoomId());
int id = roomRepository.findRoomByDate(Mockito.any(Date.class), Mockito.any(Date.class), Mockito.anyString());
assertEquals(1, id);
}
}

Answer 1

Instead of mocking the database fetch function, you can just use the embedded database setup with some annotations. It helps us to test the query efficiently. If you are using an in-memory database(embedded) first you have to add (save) entry in the table. Then your query function should fetch the data. With the help of this you can easily debug the null pointer exceptions.
Eg:
#SpringBootTest
#AutoConfigureTestDatabase
#ContextConfiguration(locations = { "classpath*:resources/invoices-context.xml",
"classpath*:resources/invoices-int-schema.xml" })
public class RoomRepositoryTest {
#Autowired
RoomRepository roomRepository;
private RoomEntity roomEntity;
#Test
public void findRommByDateTest() throws ParseException {
String startDate = "27-07-2020";
sDate = new SimpleDateFormat("dd-mm-yyyy").parse(startDate);
String endDate = "28-07-2020";
eDate = new SimpleDateFormat("dd-mm-yyyy").parse(endDate);
String roomType = "SINGLE";
roomEntity = new RoomEntity();
roomEntity.setRoomId(1);
roomEntity.setRoomPrice(6000);
roomEntity.setRoomStatus("AVAILABLE");
roomEntity.setRoomType("SINGLE");
//adding data for testing
roomRepository.save(roomEntity)
//test the actual function
int id = roomRepository.findRoomByDate(sDate,eDate);
assertEquals(1, id);
}